Signaling system



ly 14, 1931- J. c. SCHEYLLENG 1,813,961

SIGNALING SYSTEM Filed Aug. 28, 1925 2 Sheets-Sheet 1 y 1931. J. c; SCHELLENG 1,813,961

SIGNALING SYSTEM Filed 28, 1925 2 Sheets-Sheet z Patented July 14, 1931 UNITED STATES PATENT OFFICE 1 JOHN C. SGHELLENG, OF MILL-BURN, NEW JERSEY, ASSIGNOR T0 WESTERN ELECTRIC COMPANY, INCORPGEATED, OF NEW YQRK, N. Y., A CORPORATION OF NEW YORK SIGNALING SYSTEM 7 7 Application filed August 28, 1925.

This invention relates to signaling systems and more particularly to a three-phase directional transmission system.

In directional transmission systems heretofore proposed a common method of controlling the direction in which the waves are propagated is by means of a reflector. In one particular type of system, a parabolic reflector is used in the focus of which is placed. the radiating member. This: will effectively cutoff the waves in one direction and will propagate a more or less parallel beam in the direction in which the reflector faces.

British Patent 226,246, June 21, 1923, discloses a system in which a multiple tuned antenna is used as-a source of radiated waves. A second multiple tuned antenna, located a certain distance from and parallel to the first antenna, serves as a reflector to effectively neutralize waves radiated in one direction and to enable the system to be directive in the opposite direction.

In the above mentioned systems the cur-,

rentin the reflecting members is produced by the field radiated by the'primary aerial. This current is less than the current in the primary aerial due to the resistance and other'losses of the system, consequently com-v plete neutralization does not occur.

To effect complete neutralization it is desirable to provide means for directly applying energy in proper phase relationship to the reflecting members to insure that the currents in the various aerials will be equal. A poly-phase power supply is well adapted to such a use as currents of the variousj phases may be applied to the different aerials to produce the desired result.

It is an object of this invention to provide for efiicient directional radio transmission. Another object is to provide for efficient directional transmission in a three phase system.

These objects and others which will be apparent as the nature of the invention is disclosed, are. accomplished by employing in a directional transmission system, a multiple antenna system which is energized from a suitable source of poly-phase current. The

Serial No. 52,989.

antenna system consists of a plurality of similar multiple-tuned aerials or linear antenna arrays arranged in parallel planes and separated from each other by a distance which is a simple fraction of the length of the wave it is desired to transmit. Each aerial is supplied with energy from one phase of the poly-phase high-frequency source.

In order to obtain a suitable source of poly-phase high-frequency modulated current, it is proposed to employ a poly-phase space discharge oscillator which is stabilized in operation by having impressed upon it a current of a frequency which is a harmonic of the frequency at which the oscillator is to operate. Current from the oscillator is impressed upon a harmonic generator which is Although the novel features and combina- I tions which are believed to be characteristic of this invention will be pointed out with particularity in the claims appended hereto, the invention itself as to its objects and advantages, the mode of its operation and the manner of its organization will be better understood by referring to the following description taken in connection with the accompanying drawings forming a part thereof in which Fig. 1 shows diagrammatically a threephase carrier current transmission system and Fig. 2 shows a three-phase antenna structure adapted to be operated in connection with the system shown in Fig. 1.

Referring to the figures more in detail, in Fig. 1 is shown a three=phase space discharge oscillator comprising space discharge devices 1 and their associated circuits. This system is similar to that shown and described in U. S. patent to Heising 1,690,226, November 6, 1928. The three oscillators are maintained in proper phase relationship by means of condensers 2 interconnected in delta, each condenser being connected between the anodes of an individual pair of the space discharge devices. Therefore, neglecting the stopping condensers which have relatively small impedances, a capacitative circuit may be traced from each anode to its corresponding cathode including each of said condensers and the anodecathode spaces of two of the devices. The capacity of this circuit is the frequency determining capacity of a tuned output type of oscillator. The corresponding inductive path of the frequency determining circuit may be similarly traced through the anode coupling coil of each device although, to a limited extent and through certain of the condensers in series therewith, the coupling coils of the other devices affect the frequency of each device. The frequencies of the several devices are made, as nearly as may be, equal. For a disclosure of the method of operation of a tnree-phase generating system based on a similar principle reference may be made to above mentioned application of Heising.

The precise frequency at which oscillators including tubes 1 will generate oscillations is controlled by a high frequency generator 3 which is so designed and constructed as to impress a wave of particularly stable frequency upon the input circuits of the varous oscillator tubes to which it is coupled by transformer a, forming part of a tuned circuit V V The high frequency generator 3 may be of any form capable of generating an extremely stable frequency. ()ne such system is shown in a copending application of J. F. Farrington filed April 7, 1925, Serial No. 21,298 in which a comparatively low frequency oscillator, adapted to operate at a very constant frequency, is used to excite a series of harmon c generators by means of which tie frequency of the current produced by the first mentioned generator is stepped up to the desired value.

The manner in which a harmonic frequency may be used to stabilize the frequency of an oscillator has been set forth and described in U. S. patent to Schelleng No. 1,527, 28, February 24, 1925'. In the system described in that patent, it is pointed out that two oscillators, adapted to gen.- erate current at harmonica-Hy related frequencies, may be kept in step by impressing upon the input of the lower frequency oscillator waves of the harmonic frequency generated by the other oscillator or a multiple thereof. A. fundamental frequency wave could be used to stabilize the fre quency of any one of the oscillator units, and therefore, through interaction between the units, to stabilize the frequency of the polyphase oscillator as a whole. However, in the present instance a harmonic of the same order as the number of phases, or an integral multiple thereof, is used, in order to symmetrically impress the maximum controlling effect on all of said oscillator units, and thereby insure optimum stabilization.

Three phase oscillations generated by tubes 1 are impressed upon tubes 6 comprising a three-phase harmonic producer. The output circuit of the harmonic producer includes tuned circuits 7 which are adapted to select a desired harmonic frequency. By this means a high frequency current is produced having a constancy of frequency determined by that of source 1.

Three-phase currents in the output circuits of tubes 6, which are harmonically related to the oscillations generated by tubes 1, are impressed by means of transformers 8, upon a three-phase amplifier consisting of space discharge devices 10. Since the process of harmonic production results at the same time in a like multiplying of the phase differences of the currents 'it follows that the third harmonic currents and multiples thereof are in equal phase and are, therefore, unsuited for the purpose of the invention; the other harmonics, however, are properly phased. As herein shown by way of illustration, a single space discharge tube for each phase is used, but any number of tubes may be connected in parallel to bring the amplifying capacity for each phase up to the desired value.

Spurious oscillations are prevented from occurring in the circuits of tubes 10 by means of balancing condensers 11 interconnecting the anodes and grids of the three tubes, whereby each grid is maintained at neutral potential with respect to the three plates and vice versa. The capacity of con densers 11 is substantially equal to the internal grid-plate capacity of the tubes.

The three-phase high-frequency highpower output wave of tubes 10 is modulated by signal frequency currents controlled by microphone 13' which is adapted to vary the space current flowing in tube 14 in the usual manner. Low-frequency choke-coil 15 provents the production of speech frequency variations in the space current supplied by the source 16, due to the impressed signals from microphone 13. Inasmuch as space current is supplied to tubes 10 and 14 in parallel and variations in the current'supplied by source 16 are prevented by choke coil 15, any increase or decrease inthe amount of space current flowing in tube 14 must be compensated by a decrease or increase in the current flowingin tubes 10 in the manner described in U. S. Patent 1,442,- 147, January 16, 1923 to R. A. Heising.

Modulated waves produced in the output circuit of tubes 10 are transmitted through transformers 12 to the outgoing channel or transmission circuits 40, 41, and 42.

Grid polarizing potential is supplied to space discharge devices 1, 6 and 10 from source 17 through potentiometers 18. High frequency choke coils 19 are adapted to prevent the high frequency oscillations from passing through source 17. Choke coils 20 in the anode circuits of the various tubes prevent high frequency oscillations from being short-circuited through the source 16 of space current.

Three-phase modulated waves transmitted through transformers 12 are impressed upon the aerial structure shown in Fig.2, comprising multiple-tuned aerials A, B and C, placed in parallel planes and spaced apart. These aerials are spaced apart in a partic- 'ular case by a distance approximately one 25' third of the length of the wave it is desired to radiate, although the spacing may be varied to meet different local conditions. Aerials A, B and C are supported from towers or masts 21, 22 and 23, respectively, and comprise vertical radiating members 24, each of which is tuned by an inductance 25, placed at the lower end thereof, and its capacity to ground, in such manner that the natural period of each of the members is equal to that of the wave radiated. Vertical members 24 are suspended from member 26, connecting the towers, by supports including tension insulators 27. The supports are so adjusted in length that the upper ends of the radiating members 24 lie in the same horizontal plane. Each aerial has a horizontal length substantially greater than the length of the wave to be radiated.

Energy is supplied from the transmission lines 40, 41 and 42 to aerials A, B and C by means of coils 28, 29 and 30 inductively coupled to coils 31, 32 and 33, respectively. The connection of the various coils is so chosen that each antenna structure is supplied with a modulated wave from one phase only of the source comprising tubes 10 and associated circuits. .The operation of the antenna system would not bevmaterially changed, and not at all in principle, if the various radiating members 24 con stituted separate and individual aerials, the combination including all of such aerials corresponding to each multiple-tuned antenna disclosed, each of such aerials having impressed on it through an individual transformer a wave from an individual one of transmission lines 40, 41 or 42.

.The radiating system operates as follows:

The separate transmission lines, 40, 41 and 42 are connected tothe secondarim of transformers '12, and the numbers 40, 41 and 42 represent the order in which the corresponding voltages across these secondaries attain a given phase, that is, the numbers represent the order in which these voltages have a maximum value, assuming that the coupling between the transmission line and the antenna is such that no reflection occurs from the antenna end of the transmission line.

Waves impressed by transformers 12 on the line, travel to the right along the transmission line with a velocity substantially equal to the velocity of a wave in free space. Referring the phases of the currents in lines 41 and 42 to that in line 40 as standard, the

current in line 41 lags one-third of a period and current in line 42 lags two-thirds of a period behind that in line 40. The longer transmission lines 41 and 42 add a further lag of one-third period and two-thirds period, respectively, so that currents in antennae B and C lag behind that in antenna A by two-thirds period and four-thirds period, respectively. Since a lag of fourthirds period is the same as a lag of onethird period in respect to interference effects produced in space, the antennae have their maxima of current in the order ABC whichis the same as CBA. This is the re-.

verse of the order at transformers 12, the reason being that different times are required for the wire wave to travel to the antennae.

It follows that no signal will be transmitted toward the right, for since the velocity of the wave along the wires is sub stantially the same as that of the wave radiated the same time is required in the three channels for the efiect of a wave to reach a given point to the right, and since at transformer 12 the total current in the three lines is zero, the eifect at points to the right is also zero. On the other hand, currents in antennae C, B and A reach a maximum in the order which is needed for these effects to add at a distant point to the left. A wave from antenna C needs an earlier start than one from antenna B for the maximum of the two radiated waves to reach the distant point at the same time. Since distance between antennae B and C equals one-third of a wave-length the phase difference of one-third of a period which has been shown to exist between antennae A and C is just what is needed.

For directions perpendicular to the plane of the paper the effect of resultant field strength of the antennae is zero, since the distances to the antennae are the samefrom a distant point, and the currents of the three antennae are in three-phase relationship.

Effects produced by any differences between the velocityalong the transmission lines and the velocity of a wave in space may be eliminated by altering the length of the transmission lines in such a manner that the antenna currents are in the proper phases.

If the order of the phases of the currents in transmission lines 4-0, 4:1 and A2, or the order of the connections from such transmission lines to the antennae is reversed it is seen that the currents in all of the antennae will be in the same phase, which is a condition for maximum signal in a di rection perpendicular to the paper and zero transmission to the left or to the right. In this case it is not desirable to employ long multiple tuned antennae. A, B and C, the proper length being small compared to a wavelength.

If the power station is connected to the three antennae by lines of equal len th the antenna arrangement shown is also unidirectional and the directions can be reversed by reversing the order of the phases as before.

With certain forms or sizes of antenna the antenna currents might differ in size or phase from those in the case described above due to the interaction which exists between the currents of the various antennae. T his effect may be compensated for by suitable selection of spacing, tuning or phase relationship. Since a three-phase source of sup ply is available it is possible to employ a large variety of phase relationships.

The purpose of using multiple-tuned antenna units or of parallel antenna arrays may be explained as follows: From one point of view the antenna system may be thought of as comprising as many sets of directive antenna systems, each comprising three vertical spaced aerials, as there are radiating members 24 in each of the multiple-tuned antennae disclosed or, considered more broadly, of as many such systems as there are individual antennae in each of antenna arrays 21, 22 and 23. These sets of directive systems superpose their effects. This indicates the desirability of using multiple-tuned antennae having a large number of radiating members at. From another point of view, and for the purpose of indicating the desirability of making each multiple-tuned antenna long as compared with the length of the wave to be radiated, each of the multiple-tuned antennae may be thought of as a directive antenna array whose purpose is to insure substantially zero radiation in either direction along its axis and a maximum radiation in directions at direct angles thereto. These desired directive properties, as is well-known, require that the array be long as compared with the war e length of the radiated waves. The fact of directivity of such arrays would be clearly apparent if the radiating members 24 were a half wave length or a multiple thereof apart. The conditions are not changed by the use of a greater number of such members spaced a lessor distance since the array may be resolved into a plurality of such elemental arrays having the. halfwave spacing. The considerations above expressed indicate the advantage of using both a large number of radiating members 24 and of using relatively long multiple-tuned antennae comprising such members.

An advantage of the system described, is that power is supplied equally to the various aerials to insure equal radiation and increase the directive properties. The directional effect may be still further increased by employing additional aerial structures and supplying them with currents in the proper phase relationship. The use of a poly-phase current generator provides means for energizing the aerials with currents in any desired phase relationship to obtain the proper directional effect without necessitating the use of phase shifting net works and filters.

The three-phase system, such as shown in Fig. 1, avoids the connection of a plurality of space discharge devices in parallel; so that the tendency of the device .to generate certain spurious oscillations is greatly decreased.

Although this invention has been shown and described as applied to a particular system, it should be understood that it is not to be limited thereto, but only in accordance with the scope of the invention as defined by the following claims.

What is claimed is:

1. In a transmission system including a plurality of multiple-tuned aerials in parallel planes and a source of polyphase currents, means for energizing each aerial with single phase current from such source in such manner that the currents in the various aerials are in different phase relationship.

2. A polyphase transmitting antenna structure comprising a source of polyphase current and a plurality of aerials connected therewith, corresponding in number to the number of phases, each comprising a linear array of substantially parallel antenna units, each tuned to the frequency of said current and connected in parallel, the planes occupied by such arrays also being in parallel with each other.

3. A directive three-phase transmitting antenna system comprising a plurality of multiple-tuned aerials in parallel planes and spaced apart by a distance approximately one-third of the length of the wave to be radiated.

l A directive polyphase transmitting antenna system comprising a plurality of multiple-tuned aerials in parallel planes, each of said aerials having a horizontal length substantially greater than the length of the wave to be radiated therefrom.

5. In a transmission system, a source of modulated polyphase currents, and a polyphase antenna structure having multiplementioned oscillations in accordance with a low frequency signaling wave, in combination with a polyphase antenna structure.

8. In a signal transmission system, a source of polyphase oscillations, means for producing polyphase oscillations harmonically related thereto, means for amplifying said last mentioned oscillations,and means for modulating said last mentioned oscillations in accordance with a low frequency signaling wave, in combination with a polyphase antenna structure, and means for impressing said modulated oscillations upon said antenna structure.

9. In a signal transmission system, a source of polyphase current comprising a plurality of space discharge oscillators having input and output circuits, means for producing oscillations harmonically related to said current, the order of the harmonic being equal to the number of phases of the current from said source or a multiple thereof, and means for impressing said oscillations upon the input circuits of said space discharge oscillators whereby the frequency of said polyphase currents is controlled, a harmonic producer comprising discharge devices for producing polyphase currents harmonically related to said first mentioned currents, a polyphase amplifier for amplifying said last mentioned currents comprising space discharge devices having anodes, cathodes and control elements, condensers connected between anode and control elements of said devices whereby the tendency to produce spurious oscillations is minimized, a source of signaling current, means for impressing said signaling currents upon the anode circuit of of said amplifier whereby a. modulated polyphase current'is produced, a polyphase antenna structure, and means for impressing said modulated currents thereon, said antenna comprising a plurality of aerials, spaced apart a distance equal to approximately one-third the length of the wave to be radiated divided by the number of phases.

10. A communication system comprising a source of modulated polyphase currents, a polyphase antenna system, and means for supplying energy derived from said currents to said antenna system, each antenna of said system comprising a linear array of unit antennm extending in a direction substantially normal to the direction of extension of the antenna system as a whole.

11. A communication system comprising a source of modulated three-phase currents, three directive antenna arrays together comprising a three-phase antenna system, and means for supplying energy derived from said currents to said antenna arrays.

12. In a system of communication including a plurality of antenna arrays, a method of transmission which comprises generating a polyphase current, modulating said current in accordance with signals, and transmitting modulated current of different phase to the respective antenna arrays.

13. In a system of communication includ ing three antenna arrays, a method of transmission which comprises generating a threephase current, modulating said current in accordance with signals, and supplying modulated current of a different phase to the respective antenna arrays.

14. A radio transmission system comprising a space discharge polyphase current source, a plurality of aerials equal in number to the number of phases, and means for energizing each aerial with a single phase current from said source in such manner that the currents in the various aerials are in diiferent phase relationship, said aerials being spaced a distance equal approximately tothe length of the wave to be radiated divided by the number of phases.

15. An oscillation generating system comprising a plurality of space discharge unit oscillators, means actuating said unit oscillators to maintain them in synchronism and in a symmetrically parallel phase relation, means for producing oscillations harmonically related to the oscillations generated by said unit oscillators, the order of the harmonic being the same .as the number of phases of the oscillations generated by said oscillators or a multiple thereof, and means for impressing the oscillations from such harmonic oscillator on the input circuits of said unit oscillators, whereby the fre- 'quency of the resultant polyphase oscillator is controlled by the frequency of the oscillations from such harmonic oscillator.

In witness whereof, I hereunto subscribe my name this 27th day of August A. D.,

JOHN C. SCHELLENG. 

